Influence of Ageing on Monocarboxylate Transporter in Human Skeletal Muscle

Abstract

Isoforms of the lactate transporter known as monocarboxylate transporter (MCT) are increased in skeletal muscle following vigorous exercise. To date, no studies have investigated how age influences the content of MCT1 and MCT4 in human skeletal muscle. PURPOSE: To test the hypothesis that, compared with the vastus lateralis (VL) of untrained subjects, the VL of endurance trained athletes would exhibit an increase in the content of MCT1 and MCT4. METHODS: Healthy male subjects (n=33) were recruited and assigned to one of six groups based on age and training status (young trained (YT), n=6, 23.2 ± 0.8 yr, young untrained (YUT), n=6, 22.3 ± 2.9 yr, middle-aged trained (MAT), n=6, 46.3 ± 4.3 yr, middle-aged untrained (MAUT), n=5, 44.6 ± 3.9 yr, senior trained (ST) n=6, 58.7 ± 3.4 yr, and senior untrained (SUT), n=4, 58.8 ± 1.9 yr. The inclusion criteria required that all trained subjects spend at least 8 hours per week training above 60% of their VO2max, and that all untrained subjects have a self-reported average of less than 3 hours per week of moderate physical activity. Assignment to training status was supported by the completion of a VO2max test, by the wearing of an Actiheart™ downloadable heart rate monitor to record daily heart rates, and by completing a physical activity questionnaire. Muscle biopsies of the VL were analyzed Western Blot for MCT1 and MCT4 content. RESULTS: There were no significant age-related differences in MCT1 or MCT4 content (Y vs. MA vs. S, P > 0.05), and no significant differences in MCT1 or MCT4 content related to training status were observed (T vs. UT, P > 0.05), although a trend toward decreased content of both isoforms was found in the untrained group when compared with the trained group. CONCLUSION: The results of this first study investigating an effect of age and training status on moncarboxylate transporters in human skeletal muscle suggest that age does not influence the level of lactate transporter proteins MCT1 and MCT4. Supported by a grant from The Gatorade Sports Science Institute.